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United States Patent |
5,342,658
|
Hong
,   et al.
|
August 30, 1994
|
Abrasion resistant silicone coating composition
Abstract
The present invention relates to an ultraviolet light curable coating
composition having a shorter curing time and an excellent abrasion
resistance, which comprises:
(A) an aqueous-alcoholic base resin dispersion containing, based on the
weight of the total solids present in the base resin dispersion,
(a) 5 to 75% by weight of a colloidal silica and
(b) 25 to 95% by weight of a partial condensate of a silanol of formula:
R SI(OH).sub.3
wherein
R is a C.sub.1-6 alkyl, C.sub.6-20 aryl or hydroxy group; and
(B) an ultraviolet light curable catalyst of formula
Ar.sub.3 S.sup.+ MX.sub.n.sup.-
wherein
Ar.sub.3 is a triphenyl, tri(4-methoxy)phenyl,
tri(3,5-dimethyl-4-hydroxyphenyl), diphenyl-2,5-dimethylphenyl or
tri(4-methyl) phenyl group; and
MX.sub.n.sup.- is a metallic halide anion.
Inventors:
|
Hong; Young J. (Daejeon, KR);
Kim; Jin B. (Daejeon, KR);
Yeo; Jong K. (Daejeon, KR)
|
Assignee:
|
Lucky Limited (Seoul, KR)
|
Appl. No.:
|
997207 |
Filed:
|
December 28, 1992 |
Foreign Application Priority Data
Current U.S. Class: |
427/515; 522/31; 522/83; 522/84; 522/172 |
Intern'l Class: |
C08G 077/08; C08G 077/16; C08J 003/28 |
Field of Search: |
522/31,83,84,172
427/515
|
References Cited
U.S. Patent Documents
3986997 | Oct., 1976 | Clark | 428/412.
|
4277287 | Jul., 1981 | Frye | 106/287.
|
4413088 | Nov., 1983 | Frye | 524/714.
|
Foreign Patent Documents |
2066278 | Jul., 1981 | GB | 522/31.
|
Other References
Chem. Abst., vol. 116, No. 8, p. 858, Abstract No. 72049j, Sakata.
|
Primary Examiner: McCamish; Marion E.
Assistant Examiner: Koeckert; Arthur H.
Attorney, Agent or Firm: Hall; James D.
Claims
What is claimed is:
1. An ultraviolet light curable coating composition, which comprises:
(A) an aqueous-alcoholic base resin dispersion containing, based on the
weight of the total solids present in the base resin dispersion,
(a) 5 to 75% by weight of a colloidal silica and
(b) 25 to 95% by weight of a partial condensate of a silanol of formula:
R Si(OH).sub.3
wherein
R is a C.sub.1-6 alkyl, C.sub.6-20 aryl or hydroxy group; and
(B) per 100 parts by weight of the toal solids of the dispersion, 0.001 to
0.02 part by weight of an ultraviolet light curable catalyst of formula:
Ar.sub.3 S.sup.+ MX.sub.n.sup.-
wherein Ar.sub.3 is a triphenyl, tri(4-methoxy)phenyl,
tri(3,5-dimethyl-4-hydroxyphenyl), diphenyl-2,5-dimethylphenyl or
tri(4-methyl) phenyl group; and MX.sub.n.sup.- is a metallic halide anion
wherein the pH of said composition ranges from 1.5 to 3.
2. The composition of claim 1 wherein 70% by weight or more of the silanol
comprises CH.sub.3 Si(OH).sub.3.
3. The composition of claim 1 wherein the catalyst is selected from the
group consisting of triphenylsulfonium hexafluoroarsenate,
tri(4-methoxyphenyl) sulfonium hexafluoroarsenate,
tri(3,5-dimethyl-4-hydroxyphenyl) sulfonium hexafluoroarsenate,
diphenyl-2,5-dimethylphenylsulfonium hexafluoroarsenate and
tri(4-methylphenyl) sulfonium hexafluoroarsenate.
4. The composition of claim 1 wherein 80% by weight or more of the alcohol
contained in the dispersion is iso-propyl alcohol.
5. The composition of claim 1 which further comprises 0.1 to 15 parts by
weight of an acid based on 100 parts by weight of the dispersion.
6. The composition of claim 5 wherein the acid is selected from the group
consisting of hydrofluoric acid, hydrochloric acid, nitric acid, sulfuric
acid and acetic acid.
7. The composition of claim 1 which further comprises 20% by weight or less
of an organic solvent based on the weight of the composition.
8. The composition of claim 7 wherein the organic solvent is selected from
the group consisting of acetone, 1,4-dioxane and methyl ethyl ketone.
9. The composition of claim 1 wherein the colloidal silica has a single
particle size or is a mixture of particles having different sizes.
10. A method for coating a substrate with the ultraviolet light curable
silicone coating composition of claim 1, which comprises applying the
composition on the substrate; exposing the coated substrate to an
ultraviolet light and thereafter, heating the exposed substrate.
11. The method of claim 10 wherein the substrate is selected from the group
consisting of polycarbonates, acrylic polymers, poly(diethylene glycol
bisallyl) carbonate, polyesters, cellulose acetate, butyrates and
acrylonitrile-butadiene-styrene.
Description
FIELD OF THE INVENTION
The present invention relates to a silicone coating composition; and, more
particularly, to a silicone coating composition capable of forming an
excellent abrasion resistant film on a substrate through an ultraviolet
light curing process.
BACKGROUND OF THE INVENTION
Recently, transparent glazing materials having a greater resistance to
shattering than glass have been widely used for various purposes. For
instance, transparent synthetic resin plates prepared from synthetic
organic polymers are used as: wind shields for trains, automobiles and
aircrafts; lenses for eye glasses and other optical devices; and window
panes in public buildings, particularly because of their lighter weight
than glass.
Despite the above advantages, however, synthetic resin plates also have
certain defects in that their surface hardness and abrasion resistance are
relatively low.
To overcome such problems, siloxane-containing coating compositions which
form an abrasion resistant coating have been developed. For example, U.S.
Pat. No. 3,986,997 discloses a heat curable coating composition, which
comprises a dispersion of colloidal silica in a lower aliphatic
alcohol-water solution of the partial condensate of a silanol of formula
R'SI(OH).sub.3 wherein R' is a C.sub.1-3 alkyl, vinyl,
3,3,3-trifluoropropyl, .gamma.-glycidoxypropyl or
.gamma.-methacryloxypropyl radical. However, this heat curable composition
has a serious drawback requiring a longer curing time than, e.g., an
acrylic functional ultraviolet light-curable coating composition.
Further, U.S. Pat. Nos. 4,348,454 and 4,201,808 disclose light-curable
acrylic functional silicone compositions. The compositions proposed in the
above patents have a shorter curing time; however, they still suffer from
the disadvantages that the preparation methods are very complicated and
the coating formed thereof has a relatively weaker abrasion resistance
when applied on a substrate.
SUMMARY OF THE INVENTION
The present inventors have made continuous efforts to overcome the
above-mentioned problems; and, as a result, have succeeded in deveoping an
ultraviolet light-curable silicone composition capable of forming a
surface coating that has a shorter curing time and yet provides a superior
abrasion resistance.
It is, therefore, an object of the present invention to provide an
ultraviolet light curable coating composition, which comprises:
(A) an aqueous-alcoholic base resin dispersion containing, based on the
weight of the total solids in the base resin dispersion,
(a) 5 to 75% by weight of a colloidal silica and
(b) 25 to 95% by weight of a partial condensate of a silanol of formula:
R Si(OH).sub.3
wherein
R is a C.sub.1-6 alkyl, C.sub.6-20 aryl or hydroxy group; and
(B) per 100 parts by weight of the total solids in the dispersion, 0.001 to
0.02 part by weight of an ultraviolet light-curable catalyst of formula:
Ar.sub.3 S.sup.+ MX.sub.n.sup.-
wherein
Ar.sub.3 is a triphenyl, tri(4-methoxyphenyl),
tri(3,5-dimethyl-4-hydroxyphenyl), diphenyl-2,5-dimethylphenyl or
tri(4-methyl) phenyl group; and
MX.sub.n.sup.- is a metallic halide anion.
It is another object of the present invention to provide a coating method
of a substrate with the ultraviolet light-curable silicone composition of
the present invention, which comprises coating the substrate with the
composition, exposing the coated substrate to an ultraviolet light and,
finally, heating the coated substrate.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A colloidal silica is a sol or stable dispersion of amorphous silica
particles. The colloidal silica can be prepared by acidifying an aqueous
solution of sodium silicate or by hydrolyzing a silicon ester or halide at
an ambient temperature. It is preferred to use the colloidal silica
generally having an average particle size ranging from 1 to 150 .mu.m,
preferably 5 to 30 .mu.m in order to obtain the dispersion having an
excellent stability. The colloidal silica may have a single particle size
or be a mixture of particles having different sizes, and is generally
employed in an amount of 5 to 75% by weight based on the weight of the
total solids in the base resin dispersion.
Such colloidal silica is well-known in the art and commercially available
such as those marketed by E. I. du Pont de Nemours & Co. under the
registered trademark of "Ludox" and by Nalco Chemical Company under the
registered trademark of "Nalcoag".
A partial condensate of silanol can be prepared by the condensation of a
silanol which may be represented by the formula RSi(OH).sub.3 (which is
preferred) or R.sub.2 Si(OH).sub.2 wherein each R may be a C.sub.1-6
alkyl, C.sub.6-20 aryl or hydroxy group, as previously defined.
The silanol can be obtained in situ by adding the corresponding
trialkoxysilane of formula RSi(OC.sub.n H.sub.2n+1).sub.3, wherein R is
the same as previously described and n is an interger of 1 to 4, to an
aqueous dispersion of colloidal silica in the presence of an acid, as will
be described in detail in Examples; and, preferably, 70% by weight or more
of the silanol is CH.sub.3 Si(OH).sub.3. Suitable trialkoxysilanes are
those containing methoxy, ethoxy, iso-propoxy and t-butoxy substituents,
which liberate the corresponding alcohol upon hydrolysis. Upon formation
of the silanol in the aqueous medium, the hydroxyl groups are subjected to
the condensation to form a siloxane bond. A minor amount of an acid such
as acetic acid may be added to promote the hydrolysis and the condensation
reactions. The condensation of the hydroxyl groups is not carried out
completely, and, therefore, some of the hydroxyl groups may still remain.
The partial condensate of silanol(b) is suitably employed in an amount of
25 to 95% by weight based on the weight of the total solids present in the
base resin dispersion.
The base resin dispersion can be preferably prepared in an alcohol-mixed
aqueous solvent as a medium. An alcohol or a mixture of more than one
alcohol may be added to the hydrolysis aqueous medium before or after the
addition of trialkoxysilane. 80% by weight or more of the alcohol
contained in the dispersion is preferably iso-propyl alcohol.
The base resin dispersion may comprise 15 to 50% by weight, preferably 25
to 40% by weight of solids, depending on the final purpose of the coating
composition.
In order to achieve the desired characteristics of the cured coating, the
base resin dispersion is preferably produced by adding a minor amount of
an acid, e.g., acetic acid as a hydrolysis catalyst to a basic colloidal
silica (if employing an acidic colloidal silica, generally the colloidal
silica is added to acetic acid); introducing a trialkoxysilane to the
resultant solution at a temperature ranging from 2.degree. to 5.degree. C.
for the hydrolysis thereof; adding a suitable amount of an alcohol, e.g.,
iso-propanol thereto; and aging the resultant alcoholic solution at a room
temperature for 1 day.
The ultraviolet light-curable catalyst of the present invention is commonly
called as `onium salt` and may be represented by Ar.sub.3 S.sup.+
MX.sub.n.sup.- wherein Ar.sub.3 is a triphenyl, tri(4-methoxy)phenyl,
tri(3,5-dimethyl-4-hydroxylphenyl), diphenyl-2,5-dimethylphenyl or
tri(4-methyl)phenyl group; and MX.sub.n.sup.- is a metallic halide anion
such as BF.sub.4.sup.- /AsF.sub.6.sup.-, PF.sub.6.sup.- or
SbF.sub.6.sup.-. The catalyst serves to break the C-S bond and to generate
an aryl radical and a strong Bronsted acid of formula HMX.sub.n wherein
MX.sub.n is a metallic halide anion described above, upon the absorption
of an ultraviolet light of a wavelength ranging from 190 nm to 365 nm,
and, therefore, functions as a cationic polymerization initiator.
Representative examples of the catalyst may include: triphenylsulfonium
hexafluoroarsenate tri(4-methoxyphenyl) sulfonium hexafluoroarsenate
tri(3,5-dimethyl-4-hydroxyphenyl) sulfonium hexafluoroarsenate
diphenyl-2,5-dimethylphenyl sulfonium hexafluoroarsenate
tri(4-methylphenyl) sulfonium hexafluoroarsenate and the like. The
catalyst is generally employed in an amount of 0.001 to 0.02 part by
weight and preferably 0.005 to 0.01 part by weight based on 100 parts by
weight of the total solids in the dispersion.
The ultraviolet light-curable coating composition of the present invention
can be easily obtained by preparing the base resin dispersion from the
colloidal silica and the partial condensate of silanol and adding the
ultraviolet light-curable catalyst and other additives thereto with
stirring. In order to mix the above components thoroughly, the catalyst
may be preferably charged in the form of a 1 wt % solution in methanol.
In addition to the above components, the coating composition of the present
invention may also comprise an acid such as hydrofluoric acid,
hydrochloric acid, nitric acid, sulfuric acid or acetic acid in an amount
of 0.1 to 15 parts by weight based on 100 parts by weight of the
dispersion for the stability of the composition.
The silicone coating composition of the present invention may further
comprise a suitable organic solvent, depending on the substrate to be
coated, in order to enhance the adhesion of the cured coating to the
substrate. For example, when polymethyl-methacrylate(PMMA) is employed as
the substrate, acetone(which is preferred), 1,4-dioxane, methyl ethyl
ketone and the like can be used. The suitable amount of the organic
solvent is 20% by weight or less based on the weight of the coating
composition. Such enhancement of the adhesion by addition of the organic
solvent is derived from the fact that the colloidal silica contained in
the composition penetrates into the swelled surface of PMMA substrate. On
the other hand, when acetone is employed, it may further act as a source
of hydrogen upon the decomposition of the `onium salt` catalyst.
The final coating composition of the present invention thus prepared is
preferably maintained at the pH of about an isoelectric point, e.g., 1.5
to 3, for the storage stability.
Hithereto, for many coating composition, the condensation reaction has been
conducted at the pH higher than an isoelectric point by using a basic
catalyst, however, the pH of the composition has been maintained at 6 to 7
for rapid curing; and, therefore, the prior composition had a poor storage
stability.
Besides the above-mentioned components, the composition of the present
invention may further comprise other additives such as surfactant,
ultraviolet absorbent, thickening agent levelling agent for modifying the
properties of the resultant cured coating.
The substrate to be coated is preferably cleaned and, optionally, primed
before the coating process begins. Thereafter, the substrate may be
applied with the coating composition of the present invention in a
thickness ranging from 1 to 15 .mu.m by using a conventional coating
method, e.g., dipping, spraying, brushing, spinning, rolling, flowing or
laminating.
Then, the substrate coated with the coating composition of the present
invention is dried at a room temperature for 3 to 10 minutes, exposed to
an ultraviolet light for 1 minute and heated for 10 to 20 minutes to cure
the coating and evaporate the solvent. The curing temperature may range
from 50.degree. to 150.degree. C., preferably 80.degree. to 130.degree. C.
and more preferably 90.degree. to 120.degree. C. The silicone coating
composition of the present invention is particularly useful for a
substrate such as polycarbonates, acrylic polymers, poly(diethylene glycol
bisallyl) carbonate, polyesters, cellulose acetate, butyrates,
acrylonitrile-butadiene-styrene and the like.
The following Examples are intended to illustrate the present invention
more specifically, without limiting the scope of the invention.
The properties of the coatings from the silicone coating compositions
prepared in Examples and Comparative Examples were evaluated by the
following methods. Unless otherewise instructed, all units, percentages,
parts, etc. as used in the Examples and Comparative Examples are by
weight.
(1) Abrasion Resistance(Taber Abrasion)
Abrasion resistance was determined by the methods in accordance with ASTM D
1044 and D 1003 as % change in haze.
(2) Scratch Resistance
Scratch resistance was measured by rubbing the surface of the coating with
No. 00 or No. 000 steel wool horizontally set on the top of a cylinder
having the diameter of 25 mm for 5 revolutions at 25 g loading, and
observing the surface of the coating visually. The results are classified
as follows:
0--not scratched
.DELTA.--scratched lightly.
X--scratched severely.
(3) Adhesion
The adhesion of the cured coating to the substrate was measured by a cross
cut cellotape peeling test, i.e., by pulling adhesive tape from a 1 mm
crosshatched grid of the coating over the surface area of 100 mm.sup.2.
This procedure was repeated three times. The results are classified as
follows:
0--not peeled.
.DELTA.--when 1-50 grids are peeled.
X--when 51-100 grids are peeled.
EXAMPLE 1
Into a reactor were charged 13.86 g of Ludox SM-30 (having the particle
size of 7 nm), 0.726 g of HS-30 (having the particle size of 12 nm) and
7.414 g of AS-40(having the particle size of 22 nm), which are the
products of E. I. du Pont de Nemours & Co.; and, 2 g of acetic acid was
added thereto. To the mixture was added dropwise 22.5 g of
methyltrimethoxysilane over 1 hour with stirring to carry out the
hydrolysis and the partial condensation reactions. 40 g of isopropanol was
added thereto and the resultant solution was aged for 24 hours.
To 100 g of the base resin dispersion thus prepared were added 3.95 g of
acetone and 3.84g of 1 wt % solution of triphenylsulonium
hexafluoroarsenate dissolved in methanol. Finally, 6.02 g of acetic acid
was added thereto with stirring to obtain the ultraviolet light-curable
coating composition of the present invention.
The coating composition thus prepared was applied on
polymethylmethacrylate, a substrate, in the thickness of about 1 .mu.m by
using the dipping method. The substrate applied with the coating
composition was dried at a room temperature for 5 minutes, exposed to
ultraviolet light for 1 minute by using Q-200001CT far-ultraviolet
exposure equipment, a product of Quintel Limited, and heated at 90.degree.
C. for 10 minutes to evaporate the solvent. The properties of the cured
coating were measured and the results are reported in Table 1.
EXAMPLE 2
The procedures described in Example I above were repeated except that said
1 wt % solution of triphenylsulfonium hexafluoroarsenate dissolved in
methanol employed was in the amount of 7.52 g.
EXAMPLE 3
The procedures described in Example 1 above were repeated except that the
second addition of acetic acid was employed in the amount of 10.15 g.
EXAMPLE 4
The procedures described in Example 1 above were repeated except that no
second addition of acetic acid was employed.
EXAMPLE 5
The procedures described in Example 1 above were repeated except that
neither acetone nor the second addition of acetic acid was used.
COMPARATIVE EXAMPLE 1
The procedures described in Example 1 above were repeated except that said
triphenylsulfonium hexafluoroarsenate solution was not employed.
COMPARATIVE EXAMPLE 2
The procedures described in Example 1 above were repeated except that 1.3 g
(0.001 mole) of choline acetate, which is a conventional heat curable
catalyst known in the art, was employed as a catalyst.
COMPARATIVE EXAMPLE 3
The procedures described in Comparative Example 1 above were repeated
except that choline acetate was replaced with 0.26 g (0.001 mole) of
sodium acetate.
COMPARATIVE EXAMPLES 4 TO 6
The procedures described in Example 1 above were repeated except that said
1 wt % solution of triphenylsulfonium hexafluoroarsenate dissolved in
methanol was employed in an amount of 10.99 g, 17.05 g and 28.84 g,
respectively.
TABLE 1
__________________________________________________________________________
Examples Comparative Examples
1 2 3 4 5 1 2 3 4 5 6
__________________________________________________________________________
Composition
Base Resin Dispersion (g)
100 100 100 100 100 100 100 100 100 100 100
Catalyst (g) 3.84
7.52
3.84
3.84
3.84 10.99
17.05
28.84
(1 wt % sol. in methanol)
Heat Choline Acetate (g) 1.3
Curing
(10 wt % sol. in isopropanol)
Catalyst
Sodium Acetate (g) 0.26
Acetone (g) 3.95
3.95
3.95
3.95 3.95
3.95
3.95
3.95
3.95
3.95
Acetic Acid (g) 6.02
6.02
10.15
Properties
Coating Formation Good
Good
Good
Good
Good
Good
Good
Good
Good
Good
Good
Scratch
# 0 0 0 0 0 0 0 0 X 0 0 .DELTA.
.DELTA.
.DELTA.
Resistance
#0 0 0 0 0 0 0 X .DELTA.
.DELTA.
X X X
Adhesion 0 0 0 0 0 .DELTA.
.DELTA.
.DELTA.
X X X
Abrasion Resistance
1.4 2.2 1.8 2.0 2.5 --.sup.1)
8.3 9.1 --.sup.1)
--.sup.1)
--.sup.1)
(Taber Abrasion)
(% change in haze)
__________________________________________________________________________
Note .sup.1) : The composions which had bad (x) Scratch Resistance with
#00 steel wool were not subjected to the test of Abrasion Resistance
As shown in Table 1, the cured coatings formed from the coating
compositions in accordance with the present invention exhibit superior
physical properties such as scratch resistance, adhesion and abrasion
resistance.
While the invention has been described in connection with the above
specific embodiments, it should be recognized that various modifications
and changes as may be apparent to those skilled in the art to which the
invention pertains may be made and also fall within the scope of the
invention as defined by the claims that follow.
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